Clinically, blindness is classified into amaurosis, cattle, hemianopsia and color blindness. According to WHO, blindness can be diagnosed when the ability to see less than 3/60 or narrowing the visual field to 10 degrees. If the visual acuity is equal to 0, we are talking about absolute blindness. At the saved light sense and reaction to changes in its intensity, but inability to distinguish the shape of the surrounding objects, blindness is called object blindness. In the civilian version of visual dysfunction, the patient can not determine the number of fingers on the hand at a distance of 3 meters. Professional blindness is also distinguished, in which vision disorders hinder the performance of professional duties.
Specific symptom of transient amaurosis is a sharp loss of vision with a total duration of no more than 10 minutes. This phenomenon is associated with reversible ischemic changes in the carotid artery pool. Leber amaurosis is manifested by nystagmus and a pronounced decrease in visual acuity, which is detected in early childhood. This form of blindness is often combined with keratoconus, cataract, astigmatism, strabismus. Ocular manifestations of the pathology are mental retardation, epileptic seizures, hearing loss, hormonal imbalance, malformations of the kidneys, bone system or CNS. Patients with this variant of blindness are rarely able to distinguish light from darkness or track the movement of nearby objects.
Pathological scotos reveal defects in the fields of vision, which the patient sees as dark spots before the eyes. These defects are able to partially close the image in question. At detection by cattle, which the patient does not notice, it is a “negative” variant of the pathology caused by the affection of optical nerve fibers. Hemianopsy is binocular blindness with lesion of one half of the fields of vision. In the homonymous form of the disease fall out both right and left halves, heteronymous binosal – lateral, heteronymous bitemporal – medial sections of the visual field. In color blindness is impaired the ability to differentiate a certain color. Protanopia is manifested by the inability to perceive the red color, tritanopia – blue-violet, deuteranopia – green. A chromatopsy is a blindness characterized by pathological color perception, in which patients are unable to distinguish all shades of the color spectrum.
Diagnosis of blindness
Diagnostics of blindness is based on visaometry, perimetry, ophthalmoscopy, fluorescent angiography, electroretinography, campimetry. Visometry allows to diagnose the degree of visual impairment. The I category includes patients with visual acuity of 0.1-0.3 DTP, II category – 0.05-0.1 DTP, III category – 0.02-0.05 DTP. Patients of IV category have preserved light sense – 0.02 Dpter, at V there is no light sense. According to the survey results, patients in the І and ²² group are classified as visually impaired. The diagnosis of blindness can be made only for persons of III-V groups. The visual field 5-10° according to the perimeter data corresponds to ІІ category, less than 5° – IV.
Also at the perimeter can be identified pathological scotoms, which have the form of visual field defects oval, rounded or arc-shaped. The method of camping in the temporal, nasal, frontal and chin points and in 4 oblique meridians measure the size of the scotoma with subsequent fixation of indicators in a special patient card. The main diagnostic method of hemyanopsy is perimetry. In a homonymous form of blindness, defects of the fields of vision are detected in the temporal and nasal regions of different eyes. Binasal variant of the pathology is characterized by the loss of medial, and bitemporal – the lateral halves of the visual field.
In case of transient amaurosis, fluorescent angiography is performed to determine the exact location of the ischemia zone. As a rule, the study allows to detect arterial embolism of the inner eyeball sheath. Leber amaurosis is characterized by a decrease in the amplitude of waves or their complete absence during electroretinography. In ophthalmoscopy in patients over 8 years of age at the periphery of the ocular fundus calcifiers and pigmented calves are determined. Ishihara test, Rabkin polychromatic tables, FALANT-test are used to diagnose color blindness.